This invention relates generally to the determination of the relative location of a probe within a human or animal body. More particularly, the present invention relates to a device and method for determining the relative location of a probe within the human or animal body by measuring or monitoring the biological impedance located adjacent to the distal end of the probe.
One type of probe generally used during endoscopic procedures is an insufflation needle. Insufflation needles are commonly known and are used during certain surgical procedures to insufflate the abdominal cavity with a vapor or gas. Typically, insufflation needles comprise an inner cannula and an outer cannula. The inner cannula extends beyond the distal tip of the outer cannula and typically has a blunt distal end. The outer cannula has a needle point with a cutting tip for easy penetration of the skin and tissue underlying the abdominal wall. The outer cannula expands into a hub section at the proximal end that houses a biasing mechanism. The inner cannula is disposed within the outer cannula and includes a hollow tube having a distal end that is normally blunt, to avoid puncturing intra-abdominal structures. The distal end of the inner cannula has a side port hole located above the distal tip of the outer cannula through which vapor or gas may flow. When the tip of the insufflation needle is subject to an axial load, as a result of contacting tissue on or within the abdominal wall, the blunt end of the inner cannula is forced within the outer cannula, exposing the sharp cutting end of the outer cannula. After the insufflation needle pierces the abdominal wall structures and enters the abdominal cavity, the inner cannula is propelled forward by the biasing mechanism. The insufflation gas is then able to be delivered through the port hole to the intra-body cavity.
The use of the insufflation needle in the typical manner has several potential drawbacks. The surgeon must estimate the location of the needle within the abdomen as the needle is being inserted. This approach can result in the accidental puncture of an intra-abdominal structure, such as the bowel, liver or major blood vessel, by the cutting tip of the outer cannula.
As the above described and other prior art systems have proven less than optimal, an object of this invention is to provide an impedance measuring system for use with a surgical probe to measure the relative impedance of intra-abdominal structures. Another object of the invention is to provide an impedance measuring system that is easily adaptable to surgical probes. Still another object of the invention is to provide a reliable means of determining whether an internal cavity has been reached. Yet another object of the invention is to provide an additional safeguard against the accidental puncture of intra-abdominal structures. Other general and more specific objects of this invention will in part be obvious from the drawings and descriptions which follow.